Tuesday, March 15, 2016

Lonsdaleite Might be a Marker for Meteor Impacts

In 1967, a hexagonal form of diamond, later named lonsdaleite, was identified for the first time inside fragments of the Canyon Diablo meteorite, the asteroid that created the Barringer Crater in Arizona.

Since then, occurrences of lonsdaleite and nanometer-sized diamonds have been speculated to serve as a marker for meteorite impacts, having also been connected to the Tunguska explosion in Russia, the Ries crater in Germany, the Younger Dryas event in sites across Northern America and more.

It has been hypothesized that lonsdaleite forms when graphite-bearing meteors strike the Earth. The violent impact generates incredible heat and pressure, transforming the graphite into diamond while retaining the graphite's original hexagonal structure. However, despite numerous theoretical and limited experimental studies, crucial questions have remained unresolved for short-time high-pressure environments relevant to meteor impacts, particularly the structural state immediately after the shock transit, the timescales involved and the influence of crystalline orientation.

In a new paper published today by Nature Communications, a team of researchers, including scientists from Lawrence Livermore National Laboratory (LLNL), provide new insight into the process of the shock-induced transition from graphite to diamond and uniquely resolve the dynamics of the phase change.